FIG. 1 shows a conventional frustrated or modulated reflective total internal reflection image display. Specifically, FIG. 1 shows a conventional so-called frustrated or modulated reflective total internal reflection (TIR) image display with a reflective porous membrane of the type described in PCT Application No. WO 2006/108285 A1 and South Korean patent No. 10-0949412. The porous membrane may also be described as a perforated film or an apertured film or combinations thereof. The terms pores, perforations and apertures will be used interchangeably forthwith.
Display 10 includes a transparent outer sheet 12 formed by partially embedding a plurality of high refractive index convex protrusions such as, for example, transparent spherical or approximately spherical beads 14 in the inward surface of a high refractive index polymeric material 12 having a flat outward viewing surface 17 by which a viewer views the display image.
An electrophoresis medium 20 is contained within a reservoir between the portions of beads 14 which protrude inwardly from material 12 and the lower sheet 24. The medium may be an inert, low refractive index, low viscosity liquid such as a fluorinated hydrocarbon. Other liquids may also be used as electrophoresis medium 20. A bead:liquid total internal reflection (TIR) interface is thus formed. Medium 20 may contain a finely dispersed suspension of light absorbing, electrophoretically mobile particles 26.
FIG. 1 also shows reflective, porous, membrane or film 140 disposed between the inward surfaces of hemisphere beads 60 and lower sheet 24 to enhance the brightness of the TIR display. The average diameter of the pores or perforations or apertures in membrane 140 may be substantially greater (e.g., about 10 times greater) than the average diameter of absorptive particles 26. The perforations in film 140 constitute a sufficiently large fraction (e.g., at least 20%) of the total surface area of membrane 140 to permit substantially unimpeded passage of absorptive particles 26 through film 140. Film 140 can be formed of a porous membrane material such as polycarbonate or fiber-weave membrane. Film 140's outward surface 142 is highly reflective, and may be either diffusely or specularly reflective. A suitably reflective membrane or film 140 can be formed from an intrinsically reflective material such as, but not limited to, a multilayer broadband reflector (e.g., Multilayer Optical Film available from 3M®, St. Paul, Minn.) or aluminized Mylar™ flexible film or by coating outward surface 142 with a reflective (e.g. aluminum) film using standard vapor deposition techniques.
In the absence of electrophoretic activity, as is illustrated to the left of dashed line 28 in FIG. 1, the smaller absorptive particles 26 tend to settle through membrane 140's pores, toward lower sheet 24. Reflectance is thus increased and enhanced since incident light rays (e.g., ray 144) which would otherwise have passed through the so-called dark pupil region of the hemisphere beads 60 and would have been absorbed, such as, by the absorptive particles 26 located at the lower sheet 24 are instead reflected (e.g., ray 146) by membrane 140's reflective outward surface 142. Light rays 148 which are incident upon reflective annular regions of the hemisphere beads are totally internally reflected as shown by exemplary ray 150.
When a voltage is applied across medium 20, as is illustrated to the right of dashed line 28 of FIG. 1, absorptive particles 26 are electrophoretically moved through membrane 140's pores to the inward surfaces of hemisphere beads 60. When so moved into this absorptive state, particles 26 absorb light ray 152 which are incident upon the annular regions of the hemisphere beads by frustrating or modulating TIR and also absorb light ray 154 which do not undergo TIR and which would otherwise pass through beads 14. Membrane 140's pores allow absorptive particles 26 to move outwardly into contact with hemisphere beads 60 in the absorptive state and to move inwardly away from hemisphere beads 60 in the reflective state, thus obscuring absorptive particles 26 from direct view in the reflective state.
FIG. 2 illustrates an exemplary prior art electrophoretic light modulator. The electrophoretic light modulator is described in U.S. Pat. No. 8,130,441. The electrophoretic light modulator 160 has an upper viewable surface 162 and a lower surface 164. The upper and lower surfaces further comprise electrode layers where the electrode on the upper surface 162 is transparent. The electrode layers on the upper and lower surface are connected by a voltage source 166. Within the void bordered by the upper 162 and lower surface 164 and electrode layers (not shown) is filled with an electrophoretic fluid 168 further having positively charged electrophoretic particles 170. Also within the void is a perforated sheet 172 with perforations 178 that may allow the particles 170 to pass through and come to rest on the upper surface 162 or lower surface 164 by an applied electrical bias by the electrode layers on the upper and lower surfaces.
By changing the bias of the electrodes, particles 170 may either shield the perforated sheet by resting on the upper surface 162 or may expose the perforated sheet by passing through the perforations 178 in the perforated sheet and resting on the lower sheet 164. The perforated sheet 172 is comprised of a reflective layer 174 to reflect light and support layer 176 where light 180 is incident on the particles 170 resting on the upper surface and mostly absorbed 182 by the particles. The dotted line 182 representing reflected light implies that only a small amount of light is reflected. When particles 170 are moved to the lower surface (not shown), the perforated sheet 172 is exposed thereby allowing light rays to reflect off 182 of the reflective surface 174. In this situation, reflected light 182 would be of much higher intensity and creating a light state of the display.